You are here: Home › Ecosystems › National Marine Sanctuaries › Tortugas Cruise 2005 › Day 6
Day 6, August 6, 2005 TER daily cruise report
Blazing sun and calm seas this morning. Intense heat on deck has us tracking any available shade as the ship's heading shifts. Five permanent stations are scheduled to be sampled today and a sixth dive will be made to retrieve a set of GPAUs.
Included among these stations are representatives of all three of our sampling strata; National Park, Tortugas Ecological Reserve and Exclusive Economic Zone. To understand why we are sampling in these three different zones a little historical background is required.
The Tortugas Banks consists of the Monument and Tortugas Banks located at the
southern margin of the shallow portion of the West Florida Shelf. In 1846
their strategic location in the Florida Straits prompted construction of
Fort Jefferson , an artillery fort, on Garden Key one of the seven islands
of the eastern bank. In 1935 the eastern bank was designated the Fort Jefferson
National Monument and in 1983 harvest of fishes within the boundaries of
the National Monument was limited to hook and line recreational fishing.
In 1992 the eastern or Monument Bank was designated as Dry Tortugas National
Park , however, fishing regulations remained unchanged. In July of 2001 the
establishment of the Tortugas Ecological Reserve, whose boundaries overlapped
with portions of the park boundaries, prompted prohibition of any harvest
of fishes in about 50% of the Park; the remaining portion remained open to
hook and line recreational fishing. The rectangular Tortugas Ecological Reserve
also overlapped the northern portion of the smaller Tortugas Bank and surrounding
shelf habitat to the north and west of the Monument Bank. Prior to the establishment
of the reserve, management of the region outside the park was based on regulations
that govern the Exclusive Economic Zone of US territorial waters. Thus, after
establishment of the Tortugas Ecological Reserve, three zones, characterized
by different fishery management, could be identified; the Exclusive Economic
Zone, where commercial and recreational harvest of fishes is permitted, the
Tortugas Ecological Reserve where all harvest of fishes is prohibited and
the Dry Tortugas National Park where harvest has been limited to hook and
line recreational fishing for 20 years and is now currently prohibited in
50% of the Park. By quantifying trends in the fishes and benthic communities
in these different zones we can assess the impact of these differing levels
of resource management. Although management of these different zones applies
mainly to fishing, changes in fish communities are expected to have a top-down
effect on the attached invertebrate, plant and algae communities. To monitor
these communities we survey two 30m transects-one on the reef, and one on
the adjacent sandy shelf. We sample along this transect using high-resolution
digital still photography and underwater video. Using these images we determine
percent cover and diversity of the various benthic habitat components-seagrasses,
algae, corals, sponges, other attached invertebrates and substrate type.
This is accomplished back at the laboratory using image analysis software.
By examining the variability of benthic coverage over the years, trends in
the health of these communities can be monitored.
Night operations were conducted in the NW corner and just outside the Reserve with the drift camera and beam trawl. Bottom was fine sand, lots of evidence of bioturbation. The beam trawl rounded up the usual suspects. One new species was observed, the pygmy sea bass.